The existence of antigonadotropins or hormones that inhibit egg development has been demonstrated in the cockroach, eye gnat, crustaceans, house fly, and mosquitoes. Such hormones can be generally characterized as oostatic hormones. In 1985, Borovsky purified an oostatic hormone 7,000-fold and disclosed that injection of a hormone preparation into the body cavity of blood imbibed insects caused inhibition of egg development and sterility in insects (Borovsky, D. [1985]Arch. Insect Biochem. Physiol. 2:333-349). Following these observations, Borovsky, D. (1988)Arch. Ins. Biochem. Physiol. 7:187-210 disclosed that injection or passage of a peptide hormone preparation into blood sucking insects caused inhibition in the biosynthesis of serine esterase, trypsin-like and chymotrypsin-like enzymes in the epithelium cells of the gut. Since trypsin is the major proteolytic enzyme synthesized in this insect (about 70-80%), the blood meal is not digested efficiently and, consequently, free amino acids needed for the synthesis of the yolk protein synthesis in the fat body are not released into the hemolymph. Yolk protein is not synthesized and yolk is not deposited in the ovaries. The result is arrested egg development in the treated insect. The oostatic hormone peptides do not have an effect when inside the gut or other parts of the digestive system (Borovsky, D. [1988], supra).
Despite the 7,000-fold purification reported by Borovsky in 1985, the oostatic hormone was not obtained in essentially pure form and no amino acid sequence had been or could be obtained. Subsequently, the isolated peptide, trypsin modulating oostatic factor (TMOF), and two analogs of that peptide, were disclosed in U.S. Pat. Nos. 5,011,909 and 5,130,253, and in a 1990 publication (Borovsky, D., D. A. Carlson, P. R. Griffin, J. Shabanowitz, D. F. Hunt [1990] FASEB J. 4:3015-3020).
It is believed that TMOF can be rapidly inactivated in the gut of a mosquito by the action of enzymes. An endopeptidase isolated from Pseudomonas fragi (Charbonneau, H. [1989] A Practical Guide to Proteins and Peptide Purification for Microsequencing (P. T. Matsudaira, ed.), Academic Press, Inc., San Diego, Calif., pp. 15-30) was shown to hydrolyze peptide bonds on the N-terminus of Asp (D). Such an enzyme may have a role in the mosquito in regulating TMOF or its analogs by hydrolyzing the N-terminus (Tyr) from the rest of the molecule, thus inactivating the hormone. Another possibility is that the hormone may be hydrolyzed by a proline iminopeptidase-like enzyme after the hormone is cleaved, or by a pronase-like enzyme that can digest polymers of L-proline (Sober, H. A. [1968] Handbook of Biochem., The Chemical Rubber Co., Cleveland, Ohio, pp. C70). Since both the N-and C-termini of TMOF are not blocked, TMOF and its analogs could be hydrolyzed by both amino- and carboxypeptides or by endopeptidases that have been shown to play an important role in the metabolism of peptide hormones in insects and mammals (Rayne, R. C., M. O'Shea [1992] Insect Biochem. Mol. Biol. 22:24-34; Schwartz, J.-C., B. Malfroy, S. De La Baume [1981] Life Sciences 29:1715-1740).
The rapid increase in pesticide resistance of disease-borne arthropods makes our hormonal approach a safer alternative to the chemical approach (e.g., synthetic pyrethroid, organochlorine, and organophosphates). However, the utility of the full-length TMOF hormone agent is limited to some extent by the rapid inactivation of this hormone by digestive enzymes.